1. Field of the Invention
The present invention relates to a stampable sheet, more specifically, it relates to a stampable sheet being excellent in heat resistance, impact resistance, dimensional stability and dielectric properties, said sheet comprising a styrene polymer having a syndiotactic configuration and a specific fibrous reinforcing material.
2. Description of the Related Arts
Recently, composite materials comprising thermoplastic resin filled with inorganic fillers as lightweight materials which are excellent in heat resistance and mechanical strength have been extensively developed. Requirements for these materials have become restricted to accommodate to diversification of their applications.
Particularly, high heat resistance and mechanical strength are required for stampable sheet which is widely used for automobile part such as a bumper, electrical and electronic part.
It has been known that sheet-like materials obtained by blending mat-like reinforcing material and polyamide, polyolefin, polyester or the like are suitable for stamping. However, the sheet utilizing polyolefin has problem that it can not sufficiently satisfy the strict restrictions for heat resistance, and the sheet utilizing polyamide, polyester or the like disadvantageously requires strict moisture control to prevent hydrolysis during molding.
Further, a composition which comprises polystyrene having a syndiotactic configuration and an inorganic filler as a composition for stampable sheet excellent in heat resistance and mechanical strength has been previously proposed (see, Japanese Patent Application Laid-Open No. 257948/1987).
However, since the above composition is obtained by melt mixing of a polystyrene having a syndiotactic configuration and an inorganic filler using a singly-screw or twin-screw extruder, long glass fibers may be ground during said melt mixing. As the result, stampable sheet molded using said composition has low impact resistance, i.e. its Izod impact strength is lower than 10 kg.cm/cm.
Recently, in the field of printed board, single-sided printed circuit board, double-sided printed circuit board, and multi-layer printed circuit board have been developed as demand for high density printed circuit board increases, and at the same time, circuit has been getting finer. With such circumstances, infrared reflow soldering has been becoming the mainstream instead of the conventional flow soldering. Using the infrared reflow soldering, the board may be exposed at higher temperature for longer period of time compared with the case using flow soldering. Thus, improvement of heat resistance such as dimensional stability, warp inhibition property and the like of the base during such soldering has been required.
As a multi-layer printed circuit board, base materials with low dielectric constant have been required in the field wherein high performance operation is required, for example, in computer.
Bumper back-up beam made of long-fiber reinforced polypropylene sheet has been proposed to overcome the defects of the conventional metallic bumper and to provide markedly lighter bumper excellent in mechanical strength especially stiffness and impact resistance. However, stiffness of such bumper is insufficient at high temperature, which is required to be improved.
As mentioned above, stampable sheet which satisfies requirements in various applications such as heat resistance, impact resistance, dimensional stability, dielectric properties has not been proposed, yet.
The present inventor has studied intensively to solve these problems of the conventional arts and to develop stampable sheet excellent in heat resistance, impact resistance, dimensional stability, dielectric properties and free from moisture control during molding which is required for the material using polyamide or polyester.